Broken quads, weird rendering?
Select your mesh.
In the object mode in the left panel of your 3D view there is bunch of options such as trnaslate and rotate and...
In Shading section you can see smooth and flat button side-by-side.
Click on flat then you'll see your mesh as it is.  

If you want to use smoth shading option, your mesh should be hi-res (at least a little bit) or it will be like what you can see in your attached image.  

Take a look at this (the same object all the time):